Samsung C27CG70 QLED monitor. It seems to have been designed to be used as a search light. In the evening and night with brightness, contrast, and all the color gun settings set to zero on the panel of the monitor itself, the image is still too bright. I have started a conversation with their support people, or perhaps all of them given the run around, but thus far they have provided no information.
Plugged into my laptop via HDMI, laptop lid closed, it is display :0
Gnome power setting has a titled section for brightness but no slider or any control for setting it. Activities bar has a slider for brightness when using the laptop, but it is gone when using the monitor.
xdotool key XF86MonBrightnessDown momentarily pops up the display gnome brightness star with a slider under it, it shows brightness slider at minimum, and it does not go any lower.
xrandr is only a software brightness. It lists HDM-1 but turing brightness down just turns the monitor into glowing orb with faint writing.
xbacklight -get returns nothing, so it is not surprising that using it to turn down the backlight does nothing.
Writing the file /sys/class/backlight/intel_backlight/brightness does nothing. However, when the HDMI is unplugged from the laptop, the laptop screen uses the value that was written there.
brightnessctl has no device listed for the HDMI-1 monitor.
So, given that the usual suspects have been eliminated, does anyone know how to turn the brightness down on the monitor?